Re: C++ debugging progress

[Daniel Berlin <dan@cgsoftware.com>]

On Wed, 28 Nov 2001, Daniel Jacobowitz wrote:

> On Wed, Nov 28, 2001 at 09:31:07AM +0000, Jason Merrill wrote:
> > >>>>> "Daniel" == Daniel Jacobowitz <drow@mvista.com> writes:
> >
> > > I'll not be posting the patches for another day or two.  The way I do it now
> > > is grossly inefficient; I look through RTTI at every lookup instead of once
> > > per type.  It also depends on presence of RTTI.  There's not much I can do
> > > about that - or rather, I could, but AFAICT it would require walking the
> > > inheritance graph in the proper order and I don't have the machinery to do
> > > that easily.  I'm not heartbroken that we need RTTI for debugging though.
> >
> > So you're using the inheritance information in the RTTI rather than the debug
> > info?  That seems unfortunate.  I'm not sure why you would need to worry
> > about ordering; the debug info should tell you exactly where things are.
> > If it doesn't, it should probably be fixed.
>
> In that case, the debug info absolutely needs to be fixed.
>
> (I'm looking at stabs here.  I haven't tried to see what Dwarf2 emits
> yet.  I don't have my head wrapped around Dwarf2.  Yeah, I know, I
> should be using it.)
>
> Consider this:
>
> struct Base { int xxx; };
> struct Left : public virtual Base { int yyy; };
> struct Right : public virtual Base { int zzz; };
> struct Bottom : public Left, public Right { int bbb; };
>
> int main() { struct Bottom bzz; return 1; }
>
> The question, of course, is:  Where's bzz.xxx?
>
> Dwarf2 first:
>  <1><115>: Abbrev Number: 15 (DW_TAG_structure_type)
>      DW_AT_sibling     : <1c2>
>      DW_AT_name        : Bottom
>      DW_AT_byte_size   : 24
>      DW_AT_decl_file   : 1
>      DW_AT_decl_line   : 4
>      DW_AT_containing_type: <22e>
>  <2><128>: Abbrev Number: 16 (DW_TAG_inheritance)
>      DW_AT_type        : <22e>
>      DW_AT_data_member_location: 2 byte block: 23 0 (DW_OP_plus_uconst: 0; )
>      DW_AT_accessibility: 1     (public)
>  <2><131>: Abbrev Number: 16 (DW_TAG_inheritance)
>      DW_AT_type        : <2df>
>      DW_AT_data_member_location: 2 byte block: 23 8 (DW_OP_plus_uconst: 8; )
>      DW_AT_accessibility: 1     (public)
>  <2><13a>: Abbrev Number: 3 (DW_TAG_member)
>      DW_AT_name        : bbb
>      DW_AT_decl_file   : 1
>      DW_AT_decl_line   : 4
>      DW_AT_type        : <cd>
>      DW_AT_data_member_location: 2 byte block: 23 10 (DW_OP_plus_uconst: 16; )
>
> Do you see it?  I don't, and I'm pretty sure it's not there.

Umm, look at type 2df and 22e.
I'm going to bet money xxx is there.